1. Field of the Invention
This invention relates to angular velocity sensor devices such as an automotive control system, an automotive tipping detection system, a navigation system, and a hand-blurring preventing system for an optical instrument, which detect angular velocities.
2. Description of the Related Art
There is proposed an oscillation type angular velocity sensor device, which is produced by a micro-machine technique for purposes of size reduction and low cost. Such sensor device typically has a sensor element shown in FIG. 23. The sensor element has a sensor chip produced using an SOI substrate to have a frame portion J1. An oscillator J4 is supported by driving beams J2 and detection beams J3 to hang across the frame portion J1. An arrow a0 indicates a drive oscillation direction of the oscillator J4 and an arrow a1 indicates a detecting oscillation direction of the oscillator J4, i.e., a direction in which a Coriolis force is produced.
The oscillator J4 having a mass m is oscillated in the drive oscillation direction perpendicular to an angular velocity axis z, and the Coriolis force of 2 mV.OMEGA., which is generated in the direction perpendicular to the drive oscillation direction and the angular velocity axis z, is detected by displacement of the oscillator J4 in the Coriolis force generating direction. Here, V represents a velocity of the oscillator J4, and .OMEGA. represents an angular velocity.
In the angular velocity sensor device described above, however, material values such as a damping coefficient and a spring constant of the sensor element change in accordance with a change in ambient temperature and elapsed time. This may cause a drift of zero point of the angular velocity output value and a change in output sensitivity. To avoid these problems, the sensor device can have a function to monitor an amplitude of the oscillator J4 to thereby oscillate the oscillator J4 with a constant amplitude. The sensor device further can have a function to detect a temperature to adjust the sensitivity in accordance with the detected temperature. These functions, however, require an oscillation monitor, a temperature sensor, and circuits therefor, resulting in increased sensor size and increased cost.